1. Field of the Invention
This invention relates to a process for forming an image, and especially to a method for obtaining a relief image which comprises imagewise exposing a photo-sensitive image-forming material and subjecting it to dry development.
2. Brief Description of the Prior Art
More specifically, the invention relates to a process for forming an image, which comprises imagewise exposing a photo-sensitive image-forming material composed of a support and a photo-sensitive composition layer formed thereon, heating the exposed image-forming material in intimate contact with a peeling development carrier sheet having a plastic layer which is non-adhesive to the photo-sensitive layer at ordinary temperatures but on heating, is softened and becomes adhesive to the photo-sensitive layer, and then separating the image-forming material from the peeling development carrier sheet under heat to leave only the exposed area or the unexposed area of the photo-sensitive layer selectively on the carrier sheet and the corresponding unexposed area of the exposed area on the support, both as a separate relief image.
Many methods for forming images by the dry development of a photo-sensitive composition have been suggested heretofore which include, for example, developing an exposed photo-sensitive material by heating, a thermal-developing method by a suitable radiation ray, by treatment with a gas, by electrostatic treatment, and by the application of pressure.
One typical dry developing method is disclosed in Japanese Patent Publication No. 9663/63 which is a so-called peeling development process utilizing a photo-sensitive image-forming material composed of a support, a layer of a photo-sensitive composition on the support and a cover sheet placed on the photo-sensitive layer in which the adhesion of the photo-sensitive layer to the support and to the cover sheet changes upon exposure. After exposure, the support is peeled from the cover sheet to leave only the exposed areas of the photo-sensitive layer on the support or the cover sheet and the unexposed area on the other, both as a relief image.
The method of image formation by peeling development is operated in the dry state, and the operation is simpler than ordinary liquid development using a large quantity of water or solvent. Furthermore, it is only the image area of the photo-sensitive image-forming composition layer which remains on the support after peeling, and the non-image area is removed from the support by peeling. Accordingly, this method also has the advantage that the stabilization of the non-image area (which is essential to a photo-sensitive materials developed by an ordinary liquid developing or thermodeveloping method) that is, its fixation, can be performed simultaneously with the developing operation. Since in the peeling development method, the photo-sensitive composition in the non-image area is fixed to the peeled sheet as a solid layer, it can be disposed of easily, and this is desirable from the standpoint of environmental preservation. When the composition contains useful ingredients, they can be completely recovered and easily re-used. Thus, this processing method is advantageous from the viewpoint of saving resources, too.
Since a general procedure for image formation by peeling was published in Japanese Patent Publication No. 9663/63, a number of specific techniques have been suggested. These techniques are classified by their basic characteristics, and briefly described below.
A three-layer structure composed of a support, a photo-sensitive layer containing a photopolymerizable monomer and a cover sheet laminated to the photo-sensitive layer constitutes a very important in the art. Peeling development of this photo-sensitive material is performed by utilizing the fact that polymerization proceeds in the exposed area of the material, and therefore, the adhesion of the photo-sensitive layer to the support and to the cover sheet differs between the exposed area and unexposed area. It is described, for example, in Japanese Patent Publication No. 3193/62 (U.S. Pat. No. 3,060,024), Japanese Patent Publication No. 22901/68 (U.S. Pat. No. 3,353,955), Japanese Patent Application (OPI) No. 7728/72 (U.S. Pat. No. 3,770,438) and U.S. Pat. Nos. 3,060,023 and 3,525,615. U.S. Pat. Nos. 3,627,529, 3,591,377 and 3,607,264 disclose a similar peel-developable photo-sensitive material consisting essentially of a support, a photo-sensitive layer and a transparent cover sheet in which the photo-sensitive composition layer contains a photocurable polyester (U.S. Pat. No. 3,591,377), a photocurable olefin compound (U.S. Pat. No. 3,607,264) or a photocuring catalyst and a thiol-containing olefin polymer (U.S. Pat. 3,627,529).
The methods described above perform peeling development by utilizing changes in adhesion incident to the photochemical reaction of a photopolymerizable monomer of a photocurable compound.
Methods using other photo-sensitive compounds are also known. For example, Japanese Patent Application (OPI) No. 57819/77 discloses a method which comprises using a laminate structure composed of a sheet consisting of a support and an adhesive composition layer formed thereon, and a transparent plastic film coated with a photo-sensitive composition comprising a diazonium salt and a binder, exposing the laminate structure, and then peeling the film thereby to leave the unexposed area of the photo-sensitive composition layer on the transparent plastic film and the exposed area on the support.
Japanese Patent Application (OPI) No. 3215/78 (U.S. patent application Ser. No. 810,828, filed June 28, 1977) discloses an invention relating to a method which uses a similar sheet composed of a support and an adhesive composition layer formed thereon. A thin film layer comprising a metal or chalcogen is further provided between the support and a photo-sensitive composition layer to form a five-layer laminate structure. It utilizes the phenomenon that peeling development after exposure induces selective separation at the interface between the non-sensitive thin film layer and the support.
In the invention disclosed in Japanese Patent Application (OPI) No. 23632/78, a photo-sensitive composition containing a polyhalogen compound and a polymer having a phenol nucleus is used, and by peeling a transparent film-like material adhering to the photo-sensitive composition layer before or after exposure, an image corresponding to the exposed image is obtained on the support.
British Pat. No. 1,319,295 discloses a peeling development method which comprises laminating a heat-softenable polymeric layer and a powder capable of absorbing infrared rays to a support, exposing the resultant material to infrared rays to impart tackiness imagewise to the heat-softenable polymeric layer, and separating the polymeric layer from the support to form an image on the support.
Methods have also been published in which compounds having various characteristics are incorporated into such peel-developable photo-sensitive materials for use in special applications.
For example, U.S. Pat. No. 3,060,024 suggested the selective adhesion of a powder of a coloring agent to the unexposed area (unpolymerized area) by utilizing the tackiness of this area.
Numerous suggestions have been made as to the use of polymer images obtained by peeling development for photoresists, and have been disclosed, for example, in Japanese Patent Application (OPI) Nos. 120825/75 and 39025/76, and U.S. Pat. No. 3,660,088.
A process for producing a printing plate by peeling development of a photo-sensitive material including an inkrepellent silicone or fluorine-containing compound in a layer of a photopolymerizable or photocurable composition is disclosed, for example, in Japanese Patent Application (OPI) Nos. 94503/73, 66304/75, (W. German Patent Application (OLS) No. 2,449,172), 58105/76, 121330/76 and 134204/76.
So far, the characteristics of known techniques about image formation by peeling have been described. Heretofore, the basic principle of peeling development lies in the changing of the adhesion between the photo-sensitive composition layer and the support by light. For example, a photopolymerizable or photocurable photo-sensitive composition is used, and by a photochemical composition at the exposed area the adhesion of the photo-sensitive layer to the support is decreased or increased from that before exposure, whereby the exposed area and the unexposed area are formed as images separated on different supports. For example, Japanese Patent Publication No. 9663/63 suggested a method for forming an image which comprises exposing a photo-sensitive composition in intimate contact with a cover sheet and peeling the cover sheet by utilizing the fact that the photo-sensitive adhesive layer has suitable tackiness at room temperature.
On the other hand, Japanese Patent Application (OPI) Nos. 57819/77, 3215/78 and 141003/76, for example, disclose a method in which the adhesiveness of the photo-sensitive composition layer itself at room temperature is not essential. In such a method, the adhesiveness required for peeling development is gained by providing a pressure-sensitive adhesive layer on a peeling sheet used as a cover sheet. In these techniques, an adhesive peeling sheet is adhered intimately to the photo-sensitive composition layer before or after imagewise exposure, and then it can be peeled off. Accordingly, a broad range of selection for the characteristics of the photo-sensitive composition is possible than the aforesaid methods which use a photopolymerizable compound as a material and utilize the tackiness of the photo-sensitive composition layer itself at ordinary temperatures.
Some techniques for separating an image more effectively by heating the image-forming material at the time of peeling have been disclosed. For example, U.S. Pat. No. 3,060,023, discloses a method which comprises using a mixture of a photopolymerizable monomer and a thermoplastic polymer as a photo-sensitive composition layer, and after exposure, bringing the photo-sensitive layer into intimate contact with a receptor sheet at a temperature of at least 40.degree. C. thereby to soften the unexposed area, i.e. the unpolymerized area of the photopolymerizable monomer, selectively and to transfer the image thermally onto the receptor sheet. This technique utilizes the transfer of the unexposed area (unpolymerized area) of the thermoplastic photopolymerizable composition to the receptor sheet under heat, and it affords a number of copies by bringing the exposed photopolymerizable composition layer into contact with a suitable support to transfer the unexposed area under heat. Since in this method, a transfer image composed of the unpolymerized area is always utilized as an image, when it is desired to utilize the image obtained on the support further for a printing plate or a photoresist, it is necessary to provide an additional step of curing the transferred image by an after treatment such as exposure.
Japanese Patent Application (OPI) No. 39025/76 discloses a method which comprises imagewise exposing a three-layer image-forming material composed of a metal substrate, a layer of a photo-sensitive composition comprising an addition-polymerizable monomer and polyvinyl butyral and a cover sheet, and peeling the exposed material while heating it, thereby to induce cohesive destruction of the unexposed area (i.e., unpolymerized area) of the photo-sensitive layer and to obtain the same positive image as used in imagewise exposure on the metal substrate which image is utilized as a photoresist image.
Thus, in the conventional techniques, the heating operation is utilized only for the purpose of increasing the flowability of the unexposed area of the photo-sensitive image-forming layer in the transferring step. The specification of Japanese Patent Application (OPI) No. 3215/78 gives a description about the effect of heating before peeling in one working example. However, the photo-sensitive image-forming material used in this example includes a layer of an adhesive composition as an essential ingredient of the peeling development carrier, and the heating operation does not play an essential role in regard to the imparting of adhesiveness between the peeling development sheet and the image-forming layer.